Incomplete vs Complete Metamorphosis
Metamorphosis means changing in form or transformation of body form. In Biology, animals with metamorphosis undergo abrupt and conspicuous changes of body forms via cell growth and differentiation. Most of the insects, amphibians, and many invertebrates undergo metamorphosis. However, these animals show two types of metamorphosis known as incomplete metamorphosis and complete metamorphosis. It does not mean that one species can show both these two types, but it does mean that certain species undergo incomplete metamorphosis while others undergo complete metamorphosis.
There are three stages in incomplete metamorphosis known as Egg stage, Nymph stage, and Adult stage. An adult female lays eggs upon mating with a fertile male. An egg case covers the eggs for protection and under proper conditions, eggs hatch. The hatchlings represent the nymphal stage of the life cycle. Nymphs look mostly like adults, but smaller in size, and their food habits are same as the adults. As the nymphs develop, they shed their exoskeleton to allow the body to grow large. Usually, after four to eight moults, the nymph becomes an adult, which usually has wings. At the adult stage, they do not moult and start wandering in search of opposite sexes for mating. Therefore, having wings in that stage benefits them. Cockroach, grasshoppers, dragonflies, and bugs are some of the insects with incomplete metamorphosis with only three stages in their life cycle. Some species viz. mayflies have aquatic nymphal stages, called Naiads. They have gills in the abdomen and look very different from their adults.
In complete metamorphosis, four different stages are present in the lifecycle known as Egg stage, Larval stage, Pupal stage, and Adult stage. Eggs from a mated female reach the larval stage. Usually, larva is completely different from the adult in their shape, size, food habits… etc. Caterpillar is the larva of butterfly, and they are completely different from each other, but the germplasm in both are the same. During larval stage, they are voracious feeders and store much food inside them to be ready for the next stage of their lifecycle. Larva makes a cocoon around it and stays inside without eating and moving. This is their pupal stage, and the pupa develops into an adult during this stage. Finally, the pupal stage becomes an adult after completion of the development, and comes out of the cocoon. This stage could range from four days to many months depending of the species. However, frogs and other amphibians also undergo complete metamorphosis, but there is no stage inside a cocoon. Frogs first lay eggs, followed by tadpoles with gills and froglets with lungs and tails, finally to become an adult frog.
What is the difference between Complete and Incomplete Metamorphosis?
In comparison, there are major differences between these two processes.
• Incomplete metamorphosis has three stages, while complete metamorphosis has four stages.
• Eggs and adults are common stages in both processes, while nymphs are involved in incomplete metamorphosis. However, complete metamorphosis involves with larval and pupal stages in addition to obvious eggs and adult stages.
• Nymphs almost look similar as the adults do, and the food habits are the same in both. However, larva is completely different from the adult in body form as well as food habits.
• There is no pupal stage in incomplete metamorphosis, but complete metamorphosis does have it, and the pupa does not eat and cannot move.